On 09/30/10 02:17 PM, Seebs wrote:
On 2010-09-30, RG<rnospa...@flownet.com> wrote:
That the problem is "elsewhere in the program" ought to be small
comfort.
It is, perhaps, but it's also an important technical point: You CAN write
correct code for such a thing.
int maximum(int a, int b) { return a> b ? a : b; }
int main() {
long x = 8589934592;
printf("Max of %ld and 1 is %d\n", x, maximum(x,1));
You invoked implementation-defined behavior here by calling maximum() with
a value which was outside the range. The defined behavior is that the
arguments are converted to the given type, namely int. The conversion
is implementation-defined and could include yielding an implementation-defined
signal which aborts execution.
Again, the maximum() function is 100% correct -- your call of it is incorrect.
You didn't pass it the right sort of data. That's your problem.
(And no, the lack of a diagnostic doesn't necessarily prove anything; see
the gcc documentation for details of what it does when converting an out
of range value into a signed type, it may well have done exactly what it
is defined to do.)
Note that the mistake can be diagnosed:
lint /tmp/u.c -m64 -errchk=all
(7) warning: passing 64-bit integer arg, expecting 32-bit integer:
maximum(arg 1)
--
Ian Collins
--
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